Fermentation Control

[KB12]

Hey all,
I had an idea for a fermentation control system and wanted to bounce the idea off some other people.
The basic concept is that I want to be able to individually control the temperature of several brews during the fermentation stage. I'd like to be able to do lagers and ales, so I need to have temperature ranges between mid 30's to upper 60's (could probably deal with low 40's on the low end). I know there's a bunch of systems out there that you can plug into a fridge but I want to do several brews at a time at different temperatures and I don't want to have 4 different fridges so I don't think those will work.
Here's my idea, it's basically central air for refrigeration systems. I want to have four cabinets that can each hold a 6.5 gal fermenter. Each will have a thermistor that monitors the temperature of the brew inside the fermenter. Something (still trying to figure out what this is, possibly a microprocessor) will compare this temperature to the setting of the brew. If the difference is greater than the differential I'll then have it trigger heating or cooling. If the cooling is triggered a vent to that cabinet will open, a fan will turn on, and the refrigeration system will trigger (scrapped from a fridge). If heating is triggered similar thing will happen with heating elements instead.
The above is one of my ideas. Some of the issues that occurred to me with this system is that there could be thermal lag to the thermistor in the fermenter. Second, air in isn't the best at transferring heat. So, the second idea that I had was to use water instead.
To explain further, the second idea is to immerse the fermenters in a water bath. Instead of regulating the temperature inside the fermenter I'd regulate the temperature of the water bath; since the conductivities are higher I think it is safe to assume they are about the same temperature (especially if something is moving the water around). Obviously this would mean heating an cooling the water instead of air, but I don't think this would be too much more difficult.
So the question are, has anyone immersed their fermenters in water to help regulate the temperature? This would also increase the thermal mass so might help keep it more stable? Secondly, if I go with this approach, I'd need some automated valves, I know solenoids are pretty good at this but the only one's I've found are pretty pricey, anyone know of cheaper electronically controlled valves? Any input/ideas would be helpful, still in the theoretical stage...

~ KB12

 

[TwoHeadsBrewing]

I've been thinking about a system like this myself, but more like a multi-chambered fridge. I was only thinking about a two-chamber design...one for 65F and one for 50F. The first chamber would be where the the fridge vent or freezer coil would be, basically the coldest chamber. The second chamber would be separated by a wall of styrofoam insulation, with a small fan mounted in the wall. When the temperature in the warmer chamber dropped below threshold, the fan would kick in an pull air from the cooler chamber.

Should be fairly easy to build a two-chamber design, but I'm not sure about a 4-chamber. Seems like a fun project, but I'm not sure if the cost of building it is worth it. For the cost of materials it would be pretty easy to find a free or very cheap fridge and just attach a temp controller.

 

[KB12]

I'm hoping to get my school to pay for some of the electronics as a 'mechatronics' project. I could go multiple fridges but as you pointed out, my project sounds more fun.

~ KB12

 

[TwoHeadsBrewing]

well, hell if the department will pay some or all of the cost and you can do this as a semester project...GO FOR IT! I'd be on that in a heartbeat if that were the case. Had a friend who just graduated with a degree in mechanical engineering, and he got to work on some pretty cool projects. In retrospect, I think I would have enjoyed mech. engineering as much as computer science.

 

[shafferpilot]

I've considered several similar systems. On the cooling side of things, I think I read somewhere on hbt about what I think is the best possible system. In a freezer you have a couple gallon container of antifreeze. In the container is an aquarium pump, or in your case several of them. The pump pushes antifreeze through a jacket or coil of copper tube which encases the fermenter and returns to the container.

The problem you face with an air conditioner based system is freeze up. A/C units aren't intended to reach the low temps you want and will condense and freeze the water vapor from the air. The controller won't turn it off because the temp in the fermenter doesn't drop, and by the time you realize that your ferment is out of control, the A/C unit has turned into a HUGE block of ice. In my fermentation cabinet, I solved this by placing the temp probe on the cooling coils and setting the controller to stay above 32F. But obviously that doesn't work for your concept

Hey, you could use the guts of an A/C after all. If you submerge the cooling coil of the A/C in an insulated container of antifreeze with it's own temp controller, it could keep the antifreeze at a much lower temperature than your average freezer, say -40F. Then when the pump pushed that stuff through the fermenter coil, it would quickly adjust the temp in the fermenter

 

[jas0420]

I did something sort of along these lines.... 3 chambers for fermenting at individual temps, one to cool water that I pump through one of three radiators in each of my fermentation chambers. Each chamber has its own set of temperature sensors that eventually tie to a relay that toggles on/off the correct pump and fan combination to move cold water into the right radiator. From there, fans pull the warmer air through the now chilled radiator, dropping the temp in that chamber.

Has worked well, but I still need to actually finish two of the chambers, so it hasn't been tested with a full load yet.

More details here.

 

[Chriso]

I've been thinking of the same kind of idea. I don't have "good" electricity, so my kitchen fridge + my kegerator are already straining my house. But I want to get up to 3 or 4 temp-controlled fermentation chambers so that I can ferment at 4 different temps if I desire. So far the closest I've come is 4 seperate mini-fridges big enough to hold an Ale Pail.